dseuss/mpnum

\directlua{mpt.defaults['tensor_width'] = 1.5}
\directlua{mpt.defaults['len_horizontal_legs'] = 1}

\directlua{mpt.draw_mpa(1, {E=1, W=1}, {x=-2.5, tensor_name='C'})}
\node at (C_1) {$C_{ij}$};
\node [anchor=north] at (C_1_W1) {$i$};
\node [anchor=north] at (C_1_E1) {$j$};

\directlua{mpt.draw_mpa(2, {E=1, W=1}, {x=2.5, tensor_name='A'})}
\node at (A_1) {$A_{ik}$};
\node [anchor=north] at (A_1_W1) {$i$};
\node [anchor=north] at (A_1_E1e) {$k$};
\node at (A_2) {$B_{jk}$};
\node [anchor=north] at (A_2_E1) {$j$};

\node at (0,0) {\Huge $=$};